U.S. patent application number 11/915201 was filed with the patent office on 2009-02-19 for cu-mo substrate and method for producing same.
This patent application is currently assigned to NEOMAX MATERIALS CO., LTD.. Invention is credited to Masaaki Ishio, Fumiaki Kikui, Kazuhiro Shiomi, Masayuki Yokota.
Application Number | 20090045506 11/915201 |
Document ID | / |
Family ID | 37451950 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090045506 |
Kind Code |
A1 |
Yokota; Masayuki ; et
al. |
February 19, 2009 |
Cu-Mo SUBSTRATE AND METHOD FOR PRODUCING SAME
Abstract
A Cu--Mo substrate 10 according to the present invention
includes: a Cu base 1 containing Cu as a main component; an Mo base
having opposing first and second principal faces 2a, 2b and
containing Mo as a main component, the second principal face 2b of
the Mo base 2 being positioned on at least a portion of a principal
face 1a of the Cu base 1; and a first Sn--Cu-type alloy layer 3
covering the first principal face 2a and side faces 2c and 2d of
the Mo base 2, the first Sn--Cu-type alloy layer 3 containing no
less than 1 mass % and no more than 13 mass % of Sn.
Inventors: |
Yokota; Masayuki; (Osaka,
JP) ; Shiomi; Kazuhiro; (Osaka, JP) ; Kikui;
Fumiaki; (Osaka, JP) ; Ishio; Masaaki; (Osaka,
JP) |
Correspondence
Address: |
NIXON PEABODY, LLP
401 9TH STREET, NW, SUITE 900
WASHINGTON
DC
20004-2128
US
|
Assignee: |
NEOMAX MATERIALS CO., LTD.
Suita-shi, Osaka
JP
|
Family ID: |
37451950 |
Appl. No.: |
11/915201 |
Filed: |
May 23, 2006 |
PCT Filed: |
May 23, 2006 |
PCT NO: |
PCT/JP2006/310223 |
371 Date: |
February 13, 2008 |
Current U.S.
Class: |
257/712 ; 156/60;
257/E23.101; 428/656 |
Current CPC
Class: |
H01L 24/48 20130101;
H01L 23/3735 20130101; Y10T 156/10 20150115; H01L 2924/1305
20130101; H01L 2924/00014 20130101; H01L 2924/00 20130101; H01L
2924/00 20130101; H01L 2224/45124 20130101; H01L 2224/48137
20130101; H01L 23/142 20130101; H01L 2224/32225 20130101; H01L
2224/73265 20130101; H01L 2924/01079 20130101; H01L 2924/00014
20130101; H01L 2924/01019 20130101; H01L 2224/45124 20130101; H01L
2924/1305 20130101; H01L 2924/13055 20130101; H01L 2224/48091
20130101; H01L 2924/13055 20130101; H01L 2224/48091 20130101; H01L
24/45 20130101; H01L 23/3736 20130101; Y10T 428/12778 20150115 |
Class at
Publication: |
257/712 ;
428/656; 156/60; 257/E23.101 |
International
Class: |
H01L 23/36 20060101
H01L023/36; B32B 15/20 20060101 B32B015/20; B32B 37/00 20060101
B32B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2005 |
JP |
2005-149232 |
Claims
1. A Cu--Mo substrate comprising: a Cu base containing Cu as a main
component; an Mo base having opposing first and second principal
faces and containing Mo as a main component, the second principal
face of the Mo base being positioned on a principal face of the Cu
base; and a first Sn--Cu-type alloy layer covering the first
principal face and side faces of the Mo base, the first Sn--Cu-type
alloy layer containing no less than 1 mass % and no more than 13
mass % of Sn.
2. The Cu--Mo substrate of claim 1, further comprising a second
Sn--Cu-type alloy layer provided between the principal face of the
Cu base and the second principal face of the Mo base, the second
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn.
3. The Cu--Mo substrate of claim 1 or 2, further comprising an Ni
plating layer covering at least a portion of a surface of the Cu
base and the first Sn--Cu alloy layer covering the Mo base.
4. The Cu--Mo substrate of any of claim 1 or 2, wherein the first
Sn--Cu-type alloy layer has a first surface which is in contact
with the first principal face of the Mo base and a second surface
opposite from the first surface, and an Sn concentration at the
second surface is higher than an Sn concentration at the first
surface.
5. A power module comprising a semiconductor device and a heat
spreader functioning to transmit a heat of the semiconductor device
to the exterior, wherein, the heat spreader comprises the Cu--Mo
substrate of claim 4.
6. The power module of claim 5, wherein the semiconductor device is
an IGBT.
7. A method for producing the Cu--Mo substrate of claim 1 or 2,
comprising: step (a) of providing the Cu base, the Mo base, and an
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn; and step (b) of melting the Sn--Cu-type
alloy layer while the Mo base and the Sn--Cu-type alloy layer are
present in this order on the principal face of the Cu base.
8. The production method for a Cu--Mo substrate of claim 7, wherein
step (a) comprises step (a1) of providing a clad composite in which
the Cu base and the Mo base are bonded together.
9. The production method for a Cu--Mo substrate of claim 7,
wherein, step (a) comprises step (a2) of providing a clad composite
in which an Sn--Cu-type alloy layer containing no less than 1 mass
% and no more than 13 mass % of Sn is bonded on the first principal
face of the Mo base, and a further Sn--Cu-type alloy layer
containing no less than 1 mass % and no more than 13 mass % of Sn
is bonded under the second principal face; and step (b) comprises
step (b1) of melting the Sn--Cu-type alloy layer and the further
Sn--Cu-type alloy layer.
10. The production method for a Cu--Mo substrate of claim 7,
wherein, step (a) comprises step (a3) of further providing a
further Sn--Cu-type alloy layer containing no less than 1 mass %
and no more than 13 mass % of Sn; and step (b) comprises step (b2)
of melting the Sn--Cu-type alloy layer and the further Sn--Cu-type
alloy layer while the further Sn--Cu-type alloy layer, the Mo base,
and the Sn--Cu-type alloy layer are present on the principal face
of the Cu base in this order.
11. A method of producing the Cu--Mo substrate of claim 1 or 2,
comprising: step (a) of providing the Cu base, the Mo base, and an
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn; step (b) of melting the Sn--Cu-type
alloy layer while the Sn--Cu-type alloy layer is present on the
first principal face of the Mo base, thus forming an Sn--Cu-type
alloy layer which covers the first principal face and side faces of
the Mo base; and step (c) of bonding the second principal face of
the Mo base having the Sn--Cu-type alloy layer formed thereon to
the principal face of the Cu base.
Description
TECHNICAL FIELD
[0001] The present invention relates to a Cu--Mo substrate, and
more particularly to a Cu--Mo substrate which is suitably used as a
heat radiating member for a power module to be mounted in an
automobile or the like.
BACKGROUND ART
[0002] A power module, which is used for driving a motor or the
like, includes a circuit board on which a semiconductor device
(chip) (e.g., a power transistor) and a heat spreader (heat sink
member) are mounted. Recently, semiconductor devices such as IGBTs
(Insulated Gate Bipolar Transistors) which are capable of rapid
operation are mainly used.
[0003] With reference to FIG. 8, the schematic outline of a generic
power module will be described.
[0004] A power module 300 is composed of a heat radiating member
101, a circuit board 108 such as a ceramic substrate, and a
semiconductor chip 109 such as an IGBT. The circuit board 108 is a
Direct Copper Bonding substrate, in which copper-foil circuit
boards 108b and 108c are directly bonded onto both faces of a
ceramic plate 108a that is composed of alumina, aluminum nitride,
silicon nitride or the like. A solder layer 112 such as Sn--Pb is
used for bonding between the heat radiating member 101 and the
circuit board 108. A solder layer 111 such as Ag--Cu is used for
bonding between the circuit board 108 and the semiconductor chip
109.
[0005] In recent years, as circuits become more and more
highly-integrated and as semiconductor devices improve in operating
speed, the power consumption of semiconductor chips is greatly
increasing, and the amount of heat generated by chips is also
rapidly increasing. Heat generation of a chip not only detracts
from the operating speed and lifespan of a device, but also causes
considerable problems of chip peeling and breaking.
[0006] In order to solve this problem, a material used for a heat
spreader is required to have a high thermal conductivity as well as
a coefficient of thermal expansion which is substantially equal to
the coefficient of thermal expansion of the semiconductor chip. The
reason is that, if there is a large difference between the
coefficient of thermal expansion of the material of the heat
spreader and the coefficient of thermal expansion of the
semiconductor chip, the semiconductor chip may peel from the heat
spreader or break, no matter how good a thermal conductivity the
material may have.
[0007] Conventionally, as heat spreaders, composite materials each
composed of different kinds of metals are generally used, e.g.,
Cu--Mo substrates and Cu--W substrates. Such substrates are
composed of Cu having a high thermal conductivity and Mo or W,
whose coefficient of thermal expansion only has a small difference
from that of a semiconductor device of Si or the like, and
therefore they exhibit practically satisfactory values in terms of
both thermal conductivity and coefficient of thermal expansion. In
particular, Cu--Mo substrates are generally used because Mo is less
expensive than W. As Cu--Mo substrates, for example, Cu--Mo clad
composites, in each of which a Cu base and an Mo base are bonded
via rolling or the like, are generally used.
[0008] As mentioned above, a heat spreader is bonded to a circuit
board or a semiconductor device via brazing. Since Cu and Mo differ
in wettability and the like with respect to the brazing material,
the surface of a Cu--Mo substrate is usually covered with an Ni
plating layer, with the purpose of facilitating brazing and
enhancing anticorrosiveness.
[0009] However, Cu and Mo are quite different in their abilities to
allow an Ni plating layer to be formed thereon. Therefore, within
one plating bath, it is difficult to form Ni plating layers showing
excellent adhesion both on the surface of the Cu base and on the
surface of the Mo base at the same time. As is well-known, Cu
permits an Ni plating layer to be easily formed thereon, whereas Mo
is liable to oxidization and therefore a hard and brittle oxide
film may occur on its surface, thus making it difficult to form an
Ni plating layer.
[0010] For example, Patent Document 1 discloses a technique for
suppressing defects and failures such as gaps and fissures at a
bonding site between a heat spreader and a metal part. There, when
bonding a heat spreader of a Cu--Mo composite alloy with an Mo
metal part, the respective entire surfaces are subjected to
separate Ni plating treatments to provide an improved wettability
with the brazing material. However, this method requires separate
Ni plating treatments to be performed which are suited to the
respective materials, thus resulting in inferior productivity.
[0011] Alternatively, a method is generally used in which, for a
Cu--Mo substrate, a pretreatment step is performed which involves
etching the surface of the Mo substrate with red prussiate
(potassium ferricyanide) before an Ni plating layer is formed by
electroplating technique, and performing a diffusion heat treatment
after depositing a thin Au film or a thin Ni film. However,
according to this method, as will be described in connection with
the Examples set forth below, a good Ni plating layer will be
formed on the Mo substrate, but the Cu surface will become coarse
and have bulges and the like through etching, thus causing the Ni
plating layer to peel. Moreover, according to this method, many
processes must be performed prior to Ni plating, thus resulting in
a lower productivity.
[0012] On the other hand, Patent Document 2 describes a method in
which an Ni plating layer is directly formed on the surface of a
Cu--Mo substrate by using an electroless plating technique. As
compared to electroplating, electroless plating has advantages of
permitting uniform plating of a workpiece that has a complicated
shape, and providing a coating of Ni plating which is high in
hardness and excellent in abrasion resistance.
[0013] [Patent Document 1] Japanese Laid-Open Patent Publication
No. 6-344131 (Sumitomo Electric Industries, Ltd.)
[0014] [Patent Document 2] Japanese Laid-Open Patent Publication
No. 62-183132 (Fuji Electric Co., Ltd.)
DISCLOSURE OF INVENTION
Problems to be Solved by the Invention
[0015] However, as will be described in connection with the
Examples set forth below, with the method described in Patent
Document 2, it is difficult to form an Ni plating layer with good
adhesion in an exposed portion of the surface of the Mo base (i.e.,
a region of the surface of the Mo base which is not in contact with
the Cu base; hereinafter may be referred to as "exposed surface
region of the Mo base").
[0016] The present invention has been made in view of the above,
and a main objective thereof is to provide: a Cu--Mo substrate
which is suitable for use as a heat spreader of a power module,
such that an Ni plating layer with excellent adhesion can be formed
on both the surface of a Cu base and the surface of an Mo base at
the same time by performing an Ni plating for the Cu--Mo substrate
in a single plating bath; and a production method thereof. Another
objective of the present invention is to provide a power module
having a heat spreader which is formed from such a Cu--Mo
substrate.
Means for Solving the Problems
[0017] A Cu--Mo substrate according to the present invention
comprises: a Cu base containing Cu as a main component; an Mo base
having opposing first and second principal faces and containing Mo
as a main component, the second principal face of the Mo base being
positioned on a principal face of the Cu base; and a first
Sn--Cu-type alloy layer covering the first principal face and side
faces of the Mo base, the first Sn--Cu-type alloy layer containing
no less than 1 mass % and no more than 13 mass % of Sn.
[0018] A preferred embodiment further comprises a second
Sn--Cu-type alloy layer provided between the principal face of the
Cu base and the second principal face of the Mo base, the second
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn.
[0019] A preferred embodiment further comprises an Ni plating layer
covering at least a portion of a surface of the Cu base and the
first Sn--Cu alloy layer covering the Mo base.
[0020] In a preferred embodiment, the first Sn--Cu-type alloy layer
has a first surface which is in contact with the first principal
face of the Mo base and a second surface opposite from the first
surface, and an Sn concentration at the second surface is higher
than an Sn concentration at the first surface.
[0021] A power module according to the present invention is a power
module comprising a semiconductor device and a heat spreader
functioning to transmit a heat of the semiconductor device to the
exterior, wherein, the heat spreader comprises the aforementioned
Cu--Mo substrate.
[0022] In a preferred embodiment, the semiconductor device is an
IGBT.
[0023] A production method for a Cu--Mo substrate according to the
present invention is a method for producing the aforementioned
Cu--Mo substrate, comprising: step (a) of providing the Cu base,
the Mo base, and an Sn--Cu-type alloy layer containing no less than
1 mass % and no more than 13 mass % of Sn; and step (b) of melting
the Sn--Cu-type alloy layer while the Mo base and the Sn--Cu-type
alloy layer are present in this order on the principal face of the
Cu base.
[0024] In a preferred embodiment, step (a) comprises step (a1) of
providing a clad composite in which the Cu base and the Mo base are
bonded together.
[0025] In a preferred embodiment, step (a) comprises step (a2) of
providing a clad composite in which an Sn--Cu-type alloy layer
containing no less than 1 mass % and no more than 13 mass % of Sn
is bonded on the first principal face of the Mo base, and a further
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn is bonded under the second principal
face; and step (b) comprises step (b1) of melting the Sn--Cu-type
alloy layer and the further Sn--Cu-type alloy layer.
[0026] In a preferred embodiment, step (a) comprises step (a3) of
further providing a further Sn--Cu-type alloy layer containing no
less than 1 mass % and no more than 13 mass % of Sn; and step (b)
comprises step (b2) of melting the Sn--Cu-type alloy layer and the
further Sn--Cu-type alloy layer while the further Sn--Cu-type alloy
layer, the Mo base, and the Sn--Cu-type alloy layer are present on
the principal face of the Cu base in this order.
[0027] A production method for a Cu--Mo substrate according to the
present invention is a method of producing the aforementioned
Cu--Mo substrate, comprising: step (a) of providing the Cu base,
the Mo base, and an Sn--Cu-type alloy layer containing no less than
1 mass % and no more than 13 mass % of Sn; step (b) of melting the
Sn--Cu-type alloy layer while the Sn--Cu-type alloy layer is
present on the first principal face of the Mo base, thus forming an
Sn--Cu-type alloy layer which covers the first principal face and
side faces of the Mo base; and step (c) of bonding the second
principal face of the Mo base having the Sn--Cu-type alloy layer
formed thereon to the principal face of the Cu base.
EFFECTS OF THE INVENTION
[0028] In a Cu--Mo substrate according to the present invention,
the surface of an Mo base is covered with an Sn--Cu-type alloy
layer whose composition is close to that of Cu and which is
excellent in adhesion with an Ni plating layer. Therefore, the
Cu--Mo substrate can be directly subjected to an Ni plating
treatment, without having to perform separate Ni plating
treatments, whereby an Ni plating layer which is excellent in
adhesion can be formed. Furthermore, the Cu--Mo substrate according
to the present invention has a high thermal conductivity, as well
as a coefficient of thermal expansion which is substantially equal
to the coefficient of thermal expansion of semiconductor chips.
Therefore, the Cu--Mo substrate according to the present invention
is suitably used as a heat spreader functioning to transmit the
heat of a semiconductor device to the exterior, and is particularly
useful as a heat spreader for a power module. A power module having
the Cu--Mo substrate according to the present invention has
excellent heat-releasing characteristics, and is able to avoid
peeling and breaking of a semiconductor chip due to a difference in
coefficients of thermal expansion.
BRIEF DESCRIPTION OF DRAWINGS
[0029] [FIG. 1] A cross-sectional view schematically showing the
construction of a Cu--Mo substrate 10 according to a first
embodiment of the present invention.
[0030] [FIG. 2] (a) to (d) are step-by-step cross-sectional view
schematically showing a first method according to the first
embodiment.
[0031] [FIG. 3] A cross-sectional view schematically showing the
construction of a Cu--Mo substrate 20 according to a second
embodiment of the present invention.
[0032] [FIG. 4] (a) to (d) are step-by-step cross-sectional views
schematically showing a second method according to the second
embodiment.
[0033] [FIG. 5] (a) to (e) are step-by-step cross-sectional views
schematically showing a third method according to the second
embodiment.
[0034] [FIG. 6] A cross-sectional view schematically showing the
construction of a power module according to a third embodiment of
the present invention.
[0035] [FIG. 7] A photograph showing a cross section of a
Cu--Mo--Ni substrate according to Inventive Example 1.
[0036] [FIG. 8] A cross-sectional view schematically showing a
schematic outline of the construction of a generic power
module.
DESCRIPTION OF THE REFERENCE NUMERALS
[0037] 1, 11 Cu base [0038] 1a, 11a principal face of Cu base
[0039] 2, 12 Mo base [0040] 2a, 12a first principal face of Mo base
[0041] 2b, 12b second principal face of Mo base [0042] 2c, 2d, 12c,
12d side face of Mo base [0043] 3 first Sn--Cu-type alloy layer
[0044] 4, 14 Ni plating layer [0045] 5 clad composite of Cu base
and Mo base bonded together [0046] 6 Sn--Cu-type brazing alloy
material [0047] 13 Sn--Cu-type alloy layer [0048] 13a first
Sn--Cu-type alloy layer [0049] 13b second Sn--Cu-type alloy layer
[0050] 15 clad composite having Sn--Cu-type alloy layers bonded
onto both faces of Mo base [0051] 10, 20 Cu--Mo substrate [0052] 21
Cu base [0053] 22a, 22b Mo base [0054] 23a, 23b Sn--Cu-type alloy
layer [0055] 24 Ni plating layer [0056] 30 first Cu--Mo substrate
30 [0057] 31a Cu base [0058] 32a Mo base [0059] 33a, 33b
Sn--Cu-type alloy layer [0060] 34a Ni plating layer [0061] 40a,
40b, 40c, 40d second Cu--Mo substrate [0062] 50a, 50b ceramic
substrate [0063] 51, 52 solder layer such as Sn--Pb [0064] 53a, 53b
solder layer such as Ag--Cu [0065] 60a, 60b, 60c, 60d semiconductor
chip [0066] 70a, 70b Al wire [0067] 80, 300 power module [0068] 90,
120 Cu--Mo multilayer plate [0069] 91, 121 Cu base [0070] 91a, 121a
principal face of Cu base [0071] 92, 122 Mo base [0072] 92a, 122a
first principal face of Mo base [0073] 92b, 122b second principal
face of Mo base [0074] 92c, 92d side face of Mo base [0075] 93, 123
Sn--Cu-type alloy layer [0076] 100, 200 Cu--Mo--Ni substrate [0077]
101 heat radiating member [0078] 108 circuit board (ceramic
substrate) [0079] 108a ceramic plate [0080] 108b, 108c copper foil
circuit board [0081] 109 semiconductor chip [0082] 111, 112 solder
layer
BEST MODE FOR CARRYING OUT THE INVENTION
[0083] With respect to a Cu--Mo substrate that is composed of a Cu
base and an Mo base (which are quite different in their abilities
to allow an Ni plating layer to be formed thereon), in order to
provide a Cu--Mo substrate such that an Ni plating layer which is
excellent in adhesion can be formed at the same time, the inventors
have conducted various studies by paying particular attention to
brazing materials which are capable of bonding to the Cu base and
the Mo base. As a result, the inventors have found that the
aforementioned objective is attained by using an Sn--Cu-type
brazing alloy material which contains a predetermined amount of Sn
and providing an Sn--Cu-type alloy layer which at least covers an
exposed surface region of the Mo base, thus arriving at the present
invention.
[0084] Hereinafter, it will be described as to how the present
invention has been arrived at.
[0085] An Sn--Cu-type brazing alloy material to be used in the
present invention, which is identical to the brazing material
described in International Publication WO2006/16479A1 by the
present inventors, contains no less than 1 mass % and no more than
13 mass % of Sn. The above International Publication discloses a
Cu--Mo substrate having an Sn--Cu-type alloy layer formed on a
bonding surface thereof, which is obtained by placing the
aforementioned Sn--Cu-type brazing alloy material in between a Cu
base and an Mo base (bonding surface) and allowing it to be
heat-melted (hereinafter also referred to as a Cu--Mo substrate of
the prior invention). According to the prior invention, a Cu--Mo
substrate is obtained which has a small difference in coefficient
of thermal expansion from the semiconductor device and which has a
high thermal conductivity.
[0086] Later on, the inventors have found that the aforementioned
Sn--Cu-type brazing alloy material has a very excellent wettability
with the Cu base and the Mo base, and also has an excellent
adhesion with the Ni plating layer. Thus, the inventors have found
that using such a brazing material and forming an Sn--Cu-type alloy
layer which at least covers an exposed surface region of the Mo
base makes it possible to apply the same Ni plating treatment for
the Cu base also for the Cu--Mo substrate, thus arriving at the
present invention.
[0087] The Cu--Mo substrate according to the present invention
includes an Sn--Cu-type alloy layer which at least covers an
exposed surface region of the Mo base (i.e., an upper face and side
faces of Mo), and thus differs in construction from the Cu--Mo
substrate of the prior invention whose Sn--Cu-type alloy layer is
formed only at the bonding surface between the Cu base and the Mo
base. According to the present invention, the exposed surface
region of the Mo base (on which it has been difficult to form an Ni
plating layer) is covered with a predetermined Sn--Cu-type alloy
layer, thus providing an enhanced adhesion with the Ni plating
layer. Moreover, since this Sn--Cu-type alloy layer contains Sn in
the range of no less than 1 mass % and no more than 13 mass %, as
does the Sn--Cu-type alloy layer of the prior invention, the Cu--Mo
substrate according to the present invention also has the property
of the Cu--Mo substrate of the prior invention (i.e., excellent
thermal conductivity and a coefficient of thermal expansion close
to the coefficient of thermal expansion of semiconductor devices).
Therefore, the Cu--Mo substrate according to the present invention
is particularly useful as a heat spreader for a power module.
[0088] (Cu--Mo Substrate)
[0089] Cu--Mo substrates according to embodiments of the present
invention, as well as production methods thereof, will be
described.
[0090] Hereinafter, before specifically describing each embodiment
with reference to the figures, a schematic outline of the present
embodiments will be first described.
[0091] As mentioned above, the Cu--Mo substrate of the present
embodiments is characterized in having a predetermined Sn--Cu-type
alloy layer which at least covers an exposed surface region of the
Mo base (i.e., a portion which is not bonded to the Cu base).
[0092] Typical examples of the Cu--Mo substrate are, for example: a
substrate having a first Sn--Cu-type alloy layer provided on an
upper face and side faces of an Mo base, as shown in FIG. 1
described below; and a substrate having a second Sn--Cu-type alloy
layer further provided between an Mo base and a Cu base (bonding
surface), as shown in FIG. 3 described below.
[0093] A preferable production method for the Cu--Mo substrate
according to the present embodiments includes: step (a) of
providing a Cu base, an Mo base, and an Sn--Cu-type alloy layer
containing no less than 1 mass % and no more than 13 mass % of Sn;
and step (b) of melting the Sn--Cu-type alloy layer while the Mo
base and the Sn--Cu-type alloy layer are present in this order on a
principal face (upper face) of the Cu base.
[0094] This method involves sequentially placing an Mo base and an
Sn--Cu-type alloy layer on the upper face of a Cu base, and melting
the Sn--Cu-type alloy layer to form a first Sn--Cu-type alloy layer
which covers the surface of the Mo base, and optionally a second
Sn--Cu-type alloy layer. Herein, the "Sn--Cu-type alloy layer"
which is placed on the Mo base contains an Sn--Cu-type brazing
alloy material to be used for composing the intended first and
second Sn--Cu-type alloy layers. There is no particular limitation
as to the shape of the Sn--Cu-type brazing alloy material, which
may be a brazing material in e.g. powder or foil form, or a molding
(e.g., a rolled material) that has been worked into a predetermined
shape.
[0095] As will be specifically described later, first to third
methods set forth below may be specific examples. It is not
intended that the production method according to the present
embodiments be limited thereto.
[0096] A first method involves: providing a clad composite in which
a Cu base and an Mo base are bonded together (step (a1)); and
placing an Sn--Cu-type alloy layer on this clad composite (or
strictly speaking, on the upper face of the Mo base) and melting
the Sn--Cu-type alloy layer. According to the first method, a first
Sn--Cu-type alloy layer which covers an upper face and side faces
of the Mo base is formed (see FIG. 2 described below).
[0097] A second method involves: providing a clad composite having
Sn--Cu-type alloy layers bonded to both faces of an Mo base (step
(a2)); and melting these Sn--Cu-type alloy layers. According to the
second method, first and second Sn--Cu-type alloy layers are formed
on an upper face and side faces of the Mo base and in between the
Mo base and the Cu base (see FIG. 4 described below).
[0098] A third method involves: placing Sn--Cu-type alloy layers in
between a Cu base and an Mo base as well as on an upper face of the
Mo base (step (a3)); and melting them. According to the third
method, as in the second method, first and second Sn--Cu-type alloy
layers are formed so as to cover all surface of the Mo base (see
FIG. 5 described below).
[0099] Another preferable production method for the Cu--Mo
substrate according to the present embodiments includes: step (a)
of providing a Cu base, an Mo base, and an Sn--Cu-type alloy layer;
step (b) of, while placing an Sn--Cu-type alloy layer on an upper
face of the Mo base, melting the Sn--Cu-type alloy layer so as to
form an Sn--Cu-type alloy layer which covers an upper face and side
faces of the Mo base; and step (c) of bonding a lower face of the
Mo base (on which the Sn--Cu-type alloy layer is formed) to the Cu
base.
[0100] This method involves melting an Sn--Cu-type alloy layer(s)
placed on an upper face or both faces of an Mo base so as to form
an Sn--Cu-type alloy layer which covers at least a portion of the
surface of the Mo base, and then bonding this Mo base to a Cu base.
For example, a specific method may involve placing an Sn--Cu-type
alloy layer on an upper face of an Mo base and melting it to form
an Sn--Cu-type alloy layer which covers the upper face and side
faces of the Mo base, and thereafter placing a further Sn--Cu-type
alloy layer between the Mo base and the Cu base and melting it.
According to this method, a Cu--Mo substrate is obtained in which
first and second Sn--Cu-type alloy layers are formed so as to cover
all surface of the Mo base. Alternatively, Sn--Cu-type alloy layers
may be placed on both faces of an Mo base, and melted to form
Sn--Cu-type alloy layers which cover all surface of the Mo base,
which may then be bonded to a Cu base.
[0101] Hereinafter, with reference to the figures, the construction
and production method of Cu--Mo substrates according to the present
embodiments will be specifically described.
Embodiment 1
[0102] With reference to FIG. 1, a Cu--Mo substrate 10 according to
a first embodiment of the present invention will be described. The
surface of the Cu--Mo substrate 10 is covered with an Ni plating
layer 4. Hereinafter, for convenience of explanation, a substrate
before having any Ni plating layer formed thereon will be referred
to as a "Cu--Mo substrate", whereas a substrate having an Ni
plating layer that covers a Cu--Mo substrate will be referred to as
a "Cu--Mo--Ni substrate".
[0103] The Cu--Mo substrate 10 of the present embodiment includes:
a Cu base containing Cu as a main component (which may hereinafter
be simply referred to as a "Cu base") 1; an Mo base containing Mo
as a main component (which may hereinafter be simply referred to as
an "Mo base") 2; and a first Sn--Cu-type alloy layer 3.
[0104] The Mo base 2 has a first principal face 2a and a second
principal face 2b that oppose each other, such that the second
principal face 2b of the Mo base 2 is positioned on a principal
face 1a of the Cu base 1. Hereinafter, for convenience, the first
principal face 2a of the Mo base may be referred to as "an upper
face of the Mo base 2", and the second principal face 2b "a lower
face of the Mo base 2". Although FIG. 1 illustrates an exemplary
Cu--Mo substrate in which the Mo base 2 is locally present on the
Cu base 1, this is not a limitation. For example, an Mo base 2
having generally the same length 2L as the length 1L of the Cu base
may be placed on the Cu base 1. This similarly applies to the
below-described embodiments.
[0105] As shown in FIG. 1, the Cu--Mo substrate 10 of the present
embodiment is characterized in that a first Sn--Cu-type alloy layer
3 is provided so as to cover an exposed surface region of the Mo
base 2 (i.e., a first principal face 2a and side faces 2c and 2d of
the Mo base 2).
[0106] The first Sn--Cu-type alloy layer 3 contains no less than 1
mass % and no more than 13 mass % of Sn. By controlling the amount
of Sn contained in the first Sn--Cu-type alloy layer 3 to be 1 mass
% or more, it becomes possible to obtain a Cu--Mo substrate which
has excellent thermal conductivity and a coefficient of thermal
expansion that is close to the coefficient of thermal expansion of
semiconductor devices and which also shows excellent adhesion with
the Ni plating layer.
[0107] An Sn--Cu-type alloy layer having an Sn content of 1 mass %
or more has a good wettability with respect to Ni. An Sn content of
2 mass % or more would be preferable for obtaining a particularly
excellent wettability. On the other hand, if the Sn content exceeds
13 mass %, the Sn--Cu-type alloy layer will become brittle, whereby
breaking and cracking may become liable to occur. Moreover, if the
Sn content exceeds 13 mass %, the Sn in the Sn--Cu-type alloy layer
will be eluted into the coating of Ni plating during plating, or
the Sn may be oxidized, whereby voids (vacancies) may occur in the
coating of Ni plating. If voids occur in the coating of Ni plating,
bulging or peeling of the film of Ni plating may occur. In order to
effectively prevent voids, it is preferable that the Sn content in
the Sn--Cu-type alloy layer 3 is 5 mass % or less.
[0108] As mentioned above, by controlling the Sn content in the
first Sn--Cu-type alloy layer 3 to be no less than 2 mass % and no
more than 5 mass %, the Sn--Cu-type alloy layer will have a
particularly good wettability with respect to Ni, whereby the film
of Ni plating can have an improved adhesion and the film of Ni
plating can have a uniform thickness. Moreover, voids generation
due to Sn elution and oxidation can also be prevented.
[0109] Furthermore, the Sn content will also differ along the
thickness direction of the Sn--Cu-type alloy layer. For example,
with respect to an Sn--Cu-type alloy layer 3A which was formed on
the upper face 2a of the Mo base 2, the Sn distribution in a cross
section taken along the thickness direction was examined by EPMA
(electron probe micro analyzer) analysis, which indicated that, as
shown in FIG. 7 described below, Sn existed in a high concentration
at the surface (i.e., a face opposite from the face which is in
contact with the first principal face 2a of the Mo base 2) of the
Sn--Cu-type alloy layer 3A, rather than being uniformly distributed
within the alloy layer 3A. The presumable reason why a region of
high Sn concentration (concentrated layer) is formed at the surface
of the Sn--Cu-type alloy layer is that Sn is susceptible to
oxidization, and therefore will migrate toward the surface of the
Sn--Cu-type alloy layer during the process of forming the
Sn--Cu-type alloy layer. The detailed experimental results will be
specifically described in connection with the Examples set forth
below. This trend was also observed after forming the Ni plating
layer 4 on the Sn--Cu-type alloy layer.
[0110] The first Sn--Cu-type alloy layer 3 contains Sn in the
aforementioned range, while the remaining parts may be composed of
Cu. However, other elements may also be contained within ranges
such that the adhesion enhancing action due to the formation of the
first Sn--Cu-type alloy layer 3 is not undermined. Examples of
other elements include elements (described later) which are
contained in the Cu base 1 and will diffuse from the Cu base 1
during the process of forming the first Sn--Cu-type alloy layer 3
(e.g., Pb, Fe, Zn, P). Such other elements may be contained
generally in the range of no less than 0.05 mass % and no more than
0.035 mass % in total.
[0111] Generally speaking, the thickness of the first Sn--Cu-type
alloy layer 3 is preferably 2 .mu.m or more, and more preferably 5
.mu.m or more, whereby the aforementioned action of the Sn--Cu-type
alloy layer will be effectively exhibited. Note that the thickness
of the first Sn--Cu-type alloy layer 3 has no particular upper
limit from the standpoint of obtaining the aforementioned action.
However, when taking into consideration cost increases and the
like, the upper limit is preferably 100 .mu.m, and more preferably
50 .mu.m, for example. Note that the thickness of the first
Sn--Cu-type alloy layer 3 is not necessarily uniform, and may have
variations depending on the surface configuration of the Mo base 2,
the method for forming the first Sn--Cu-type alloy layer 3, and the
like. Herein, it suffices if the layer thickness where the first
Sn--Cu-type alloy layer 3 is made thinnest satisfies the
aforementioned preferable range. The thickness of the first
Sn--Cu-type alloy layer 3 was measured by observing a cross section
of the alloy layer with an optical microscope.
[0112] The Cu base 1 contains Cu as a main component. By
"containing Cu as a main component", it is meant that no less than
99 mass % (and preferably no less than 99.9 mass %) of Cu is
contained. The Cu base may be composed only of Cu, or may contain
other elements within ranges such that the excellent thermal
conductivity associated with Cu is not hindered.
[0113] The Mo base 2 contains Mo as a main component. By
"containing Mo as a main component", it is meant that no less than
99 mass % (and preferably no less than 99.9 mass %) of Mo is
contained. The Mo base may be composed only of Mo, but other
elements may be contained within ranges such that Mo's
characteristically small difference in coefficient of thermal
expansion from those of semiconductor devices is not hindered.
[0114] As shown in FIG. 1, the surface of the Cu--Mo substrate 10
is covered with the Ni plating layer 4. Forming the Ni plating
layer enhances anticorrosiveness, brazability with the ceramic
substrate, and the like.
[0115] As has already been described, according to the present
embodiment, the exposed surface region of the Mo base 2 (on which
it has been difficult to directly form an Ni plating layer) is
covered with the first Sn--Cu-type alloy layer 3 having an
excellent adhesion with the Ni plating layer. Therefore, the
Cu--Mo--Ni substrate 100 can be obtained by performing a single
plating process for the Cu--Mo substrate 10.
[0116] Although the Cu--Mo--Ni substrate 100 shown in FIG. 1 has
the Ni plating layer 4 covering all surface of the Cu--Mo substrate
10, there is not limitation so long as the aforementioned action of
the Ni plating layer is effectively exhibited. For example, it
suffices so long as the first Sn--Cu-type alloy layer 3 and at
least a portion of the surface of the Cu base 1 (a portion of the
surface of the Cu base 1 where it is not covered with the Mo base 2
or the first Sn--Cu-type alloy layer 3) are covered with the Ni
plating layer 4.
[0117] Generally speaking, the thickness of the Ni plating layer 4
is preferably no less than 2 .mu.m and no more than 20 .mu.m, and
more preferably no less than 3 .mu.m and no more than 10 .mu.m. If
the thickness of the Ni plating layer 4 is below this range, the
aforementioned action will not be effectively exhibited. On the
other hand, if the thickness of the Ni plating layer 4 exceeds the
aforementioned range, the flatness of the Ni plating layer will be
lowered, so that properties such as durability will
deteriorate.
[0118] Next, with reference to FIG. 2, a preferable production
method for the Cu--Mo substrate 10 according to the present
embodiment will be described. This method corresponds to the
aforementioned first method.
[0119] (First Method)
[0120] First, as shown in FIG. 2(a), a Cu--Mo clad composite 5 in
which a Cu base 1 and an Mo base 2 are bonded together is provided
(step (a1)).
[0121] The Cu--Mo clad composite 5 can be produced by a known
method. For example, after the Cu base 1 and the Mo base 2 are
stacked together and subjected to hot rolling or cold rolling, it
is cut into a desired size according to the product dimensions. As
for a production method of the Cu--Mo clad composite 5, a method
described in Japanese Laid-Open Patent Publication No. 6-268115 may
be referred to, for example.
[0122] Next, as shown in FIG. 2(b), an Sn--Cu-type brazing alloy
material 6 is placed on the first principal face 2a of the Mo base
2, and is melted by being heated to a predetermined temperature
(step (b)). As a result, a first Sn--Cu-type alloy layer 3 is
formed which covers the exposed surface region of the Mo base 2
(i.e., the first principal face 2a and side faces 2c and 2d) (see
FIG. 2(c)).
[0123] The Sn--Cu-type brazing alloy material 6 contains no less
than 1 mass % and no more than 13 mass % of Sn. By using such an
Sn--Cu-type brazing alloy material 6, a first Sn--Cu-type alloy
layer 3 as desired can be formed. The Sn content in the Sn--Cu-type
brazing alloy material 6 is preferably no less than 2 mass % and no
more than 5 mass %.
[0124] The Sn--Cu-type brazing alloy material 6 used for the
present embodiment contains Sn in the aforementioned range, while
the remaining parts may be composed of Cu. However, other elements
may also be contained within ranges such that the adhesion
enhancing action due to the use of the Sn--Cu-type brazing alloy
material 6 is not undermined. For example, elements such as Pb, Fe,
Zn, P, and the like may be contained in an amount of no less than
0.05 mass % and no more than 0.35 mass % in total.
[0125] Heating is performed until the Sn--Cu-type brazing alloy
material 6 is melted and a first Sn--Cu-type alloy layer 3 is
formed which covers not only the first principal face 2a of the Mo
base 2 but also the side faces 2c and 2d of the Mo base 2. In this
respect, the heating condition in the present embodiment differs
from the heating condition described in the aforementioned
International Publication. The heating condition in the present
embodiment is set to be slightly higher than the lower limit value
of the heating temperature described in the aforementioned
International Publication (i.e., the melting point of the
Sn--Cu-type brazing alloy material 6). The reason is that, if the
Sn--Cu-type brazing alloy material 6 is heated only to a
temperature which is defined by the lower limit value described in
the aforementioned International Publication, an Sn--Cu alloy layer
may be formed at the bonding surface between the Cu base 1 and the
Mo base 2, but it will be difficult to form a first Cu--Sn-type
alloy layer 3 which covers the entire exposed surface region of the
Mo base 2.
[0126] The specific heating condition may depend on the type,
shape, etc. of the Sn--Cu-type brazing alloy material 6 used, but
the heating is preferably performed in a range of no less than
about 20.degree. C. and no more than about 50.degree. C., and more
preferably no less than about 40.degree. C. and no more than about
50.degree. C., above the melting point (about 810.degree. C. to
about 1000.degree. C.) of the Sn--Cu-type brazing alloy material 6.
However, the upper limit of the heating temperature is a
temperature less than the melting point (about 1083.degree. C.) of
the Cu base 1. If the heating were performed at a temperature
exceeding the melting point of the Cu base 1, the Cu base 1 would
be melted.
[0127] There is no particular limitation as to the shape of the
Sn--Cu-type brazing alloy material 6 used in the present
embodiment. Any molding which has been worked into a predetermined
shape, or a brazing material in powder or foil form, etc. may be
possible.
[0128] FIG. 2(b) illustrates an exemplary molding which has been
worked into a predetermined shape as the Sn--Cu-type brazing alloy
material 6. Such a molding can be obtained by, for example,
subjecting an Sn--Cu-type alloy of the aforementioned composition
to hot rolling at a temperature of about 650.degree. C. to about
750.degree. C., followed by molding.
[0129] In the case of using a molding of an Sn--Cu-type brazing
alloy material, after this brazing material and the Mo base 2 are
stacked together, for example, the Sn--Cu-type brazing alloy
material is preferably melted at the aforementioned temperature in
a hydrogen atmosphere, while the brazing material and the Mo base 2
are pressed at a pressure of about 10.sup.3 Pa to about 10.sup.5
Pa. Thus, the first Sn--Cu-type alloy layers 3 as desired can be
formed.
[0130] Herein, the size (length 6L) of the Sn--Cu-type brazing
alloy material 6 may be substantially the same as the size (2L) of
the Mo base 2 as shown in FIG. 2(b), but this is not a limitation.
For example, the size (length 6L) of the Sn--Cu-type brazing alloy
material 6 may be smaller than the size of the Mo base 2. As
mentioned earlier, the Sn--Cu-type brazing alloy material 6 has a
very excellent wettability with respect to the Mo base 2.
Therefore, even if an Sn--Cu-type brazing alloy material 6 which is
smaller than the Mo base 2 is placed on the Mo base 2, through a
heating at a predetermined temperature, a first Sn--Cu-type alloy 3
which covers the exposed surface region of the Mo base 2 will
eventually be formed. Thus, so long as the desired first
Sn--Cu-type alloy 3 is formed, the size of the Sn--Cu-type brazing
alloy material 6 can be selected as appropriate.
[0131] Specifically, an Sn--Cu-type brazing alloy material in
powder or foil form is placed on the upper face of the Mo base
(preplaced brazing), and is heated to the aforementioned
temperature, thus melting the brazing material. The Sn--Cu-type
brazing alloy material having been melted through the heating will
spread along the upper face and side faces of the Mo base, whereby
a desired first Sn--Cu-type alloy layer is formed.
[0132] Next, the Cu--Mo substrate 10 thus obtained is covered with
an Ni plating layer 4, thus obtaining the Cu--Mo--Ni substrate 100
(see FIG. 2(d)).
[0133] There is no particular limitation as to the method for
forming the Ni plating layer, and any known electroplating
technique or electroless plating technique may be adopted.
[0134] As compared to the electroplating technique, the electroless
plating technique has the advantage of being able to form a uniform
Ni plating layer, regardless of the type and shape of the material
to be plated (i.e., the Cu--Mo substrate in the present
embodiment). In the case of using the electroless plating
technique, it is preferable to form the Ni plating layer in the
following manner, for example.
[0135] First, in order to remove the grease, fingerprints, etc.
attached on the surface of the Cu--Mo substrate, degreasing is
performed with ethanol or the like. Through degreasing, the
wettability during etching is also improved.
[0136] Next, the surface is etched by using an etchant such as
sulfuric acid-hydrogen peroxide.
[0137] Then, a catalytic metal (e.g., Sn, Pd--Sn complex, or Pd) is
allowed to be adsorbed to the surface. The electroless plating
progresses from this catalytic metal as a core.
[0138] Next, an Ni plating layer is formed with an electroless Ni
plating solution. Specifically, the Cu--Mo substrate is immersed in
a known electroless Ni plating solution (which contains e.g. sodium
hypophosphite as a reducing agent in addition to Ni ions) until a
predetermined Ni plating layer is obtained. According to the
electroless plating technique, the Ni ions in the plating solution
are reduced as the reducing agent in the plating solution is
oxidized at the surface of the catalytic metal that has been
adsorbed to the surface of the Cu--Mo substrate, whereby an Ni
plating layer is formed.
Embodiment 2
[0139] With reference to FIG. 3, a Cu--Mo substrate 20 according to
a second embodiment of the present invention will be described.
[0140] The Cu--Mo substrate 20 of the present embodiment includes a
Cu base 11, an Mo base 12, and an Sn--Cu-type alloy layer 13. The
Mo base 12 has a first principal face 12a and a second principal
face 12b that oppose each other, such that the second principal
face 12b of the Mo base 12 is positioned on a principal face 11a of
the Cu base 11.
[0141] The Sn--Cu-type alloy layer 13 includes a first Sn--Cu-type
alloy layer (not shown) which is formed in the exposed surface
region of the Mo base 12 (i.e., the first principal face 12a and
the side faces 12c and 12d of the Mo base 12) and a second
Sn--Cu-type alloy layer (not shown) which is formed between the
second principal face 12b of the Mo base 12 and the principal face
11a of the Cu base 11. The Sn--Cu-type alloy layer 13 contains no
less than 1 mass % and no more than 13 mass % of Sn.
[0142] Thus, the Cu--Mo substrate 20 of the present embodiment
differs from the Cu--Mo substrate 10 of Embodiment 1 in that the
Sn--Cu-type alloy layer 13 is provided not only in the exposed
surface region of the Mo base 12 but also at the bonding surface
between the Mo base 12 and the Cu base 11. According to the present
embodiment, a Cu--Mo substrate is obtained which not only has an
excellent adhesion with respect to the Ni plating layer but also
shows an enhanced adhesion between the Cu base and the Mo base.
Except for this difference, the Cu--Mo substrate 20 of the present
embodiment is identical to the Cu--Mo substrate 10 of Embodiment 1,
and detailed descriptions thereof are omitted.
[0143] Furthermore, a similar trend to Embodiment 1 was observed
for the Sn distribution contained in the Sn--Cu-type alloy layer
13A formed on the upper face 12a of the Mo base 12, and it was
confirmed that Sn existed in a high concentration at the surface
(i.e., a face opposite from the face which is in contact with the
first principal face 12a of the Mo base 12) of the Sn--Cu-type
alloy layer 13A. Such a trend was also similarly observed after the
Ni plating layer 14 was formed on the Sn--Cu-type alloy layer
13.
[0144] Next, with reference respectively to FIG. 4 and FIG. 5,
preferable production methods for the Cu--Mo substrate of the
present embodiment will be described. The production steps shown in
FIG. 4 and FIG. 5 correspond to the aforementioned second and third
methods, respectively.
[0145] (Second Method)
[0146] The second method will be described with reference to FIG.
4.
[0147] First, as shown in FIG. 4(b), a clad composite (multilayer
plate) 15 is provided in which Sn--Cu-type alloy layers 13a and 13b
containing no less than 1 mass % and no more than 13 mass % of Sn
are bonded to first and second principal faces 12a and 12b of an Mo
base 12, respectively (step (a2)).
[0148] The clad composite 15 can be produced in the following
manner, for example.
[0149] First, an Sn--Cu-type brazing alloy material 16a, 16b is
provided. The details thereof are as specifically described with
respect to step (b) of Embodiment 1 above, and the description
thereof is omitted.
[0150] Next, as shown in FIG. 4(a), the Sn--Cu-type brazing alloy
material 16a, the Mo base 12, and the Sn--Cu-type brazing alloy
material 16b are stacked together in this order, and after being
pressed together at a reduction ratio of about 60%, subjected to a
diffusion anneal in a hydrogen atmosphere at a temperature of about
700.degree. C. to 800.degree. C. for about 1 minute to about 3
minutes. As a result, a clad composite 15 in which the Sn--Cu-type
alloy layers 13a and 13b are firmly bonded to both faces of the Mo
base 12 is obtained.
[0151] Next, the clad composite 15 is placed on the principal face
of the Cu base 11, and the Sn--Cu-type alloy layers 13a and 13b is
heat-melted. The heating is performed until the first and second
Sn--Cu-type alloy layers 13a and 13b formed on both faces of the Mo
base 12 are melted so that a desired Sn--Cu-type alloy layer 13 is
formed which covers all surface of the Mo base 12 (i.e., the
principal face 12a and side faces 12c and 12d of the Mo base 12 as
well as the bonding surface 12b between the Mo base 12 and the Cu
base 11). The detailed heating condition is as described in
Embodiment 1 above.
[0152] As a result, as shown in FIG. 4(c), a Cu--Mo substrate 20 is
obtained in which all surface of the Mo base 12 is covered with the
desired Sn--Cu-type alloy layer 13.
[0153] Next, in a manner similar to the aforementioned first
method, an Ni plating layer 14 is formed on the surface of the
Cu--Mo substrate 20, thus obtaining the Cu--Mo--Ni substrate 200
(see FIG. 4(d)).
[0154] (Third Method)
[0155] The third method will be described with reference to FIG. 5.
Hereinafter, steps which are different from the second method will
be specifically described, while omitting the description of any
overlapping step.
[0156] First, as shown in FIG. 5(a), a Cu base 11, an Sn--Cu-type
brazing alloy material 16b, and an Mo base 12 are placed in this
order, and the Sn--Cu-type brazing alloy material 16b is heated.
The heating is performed until the Sn--Cu-type alloy layer 13b is
formed between the Cu base 11 and the Mo base 12 (bonding surface)
(see FIG. 5(b)). The Sn--Cu-type alloy layer 13b does not need to
be formed across the entire bonding surface as shown in FIG. 5(b),
but only needs to be formed in at least a portion of the bonding
surface. The heating is preferably performed in a similar manner to
the aforementioned second method.
[0157] Next, as shown in FIG. 5(c), an Sn--Cu-type brazing alloy
material 16a is placed on a first principal face 12a of the Mo base
12, and heating is performed. The heating is performed until the
Sn--Cu-type brazing alloy material 16a is melted so that all
surface of the Mo base 12 (12a, 12b, 12c, 12d) is covered with the
Sn--Cu-type alloy layer 13. The heating condition is substantially
the same as the condition described in the second method above.
[0158] As a result, as shown in FIG. 5(d), a Cu--Mo substrate 20 is
obtained in which all surface of the Mo base 12 is covered with the
Sn--Cu-type alloy layer 13.
[0159] Next, in a manner similar to the first method above, the
surface of the Cu--Mo substrate 20 is covered with an Ni plating
layer 14, thus obtaining the Cu--Mo--Ni substrate 200 (see FIG.
5(e)).
[0160] The production method according to the present embodiment is
not limited to the second and third methods described above. For
example, in the third method, an Sn--Cu-type brazing alloy material
to which a Cu base is bonded (clad composite) may be used instead
of the Sn--Cu-type brazing alloy material 16a. As compared to using
an Sn--Cu-type brazing alloy material 16a to which a Cu base is not
bonded, this method can prevent deformation of the Sn--Cu-type
brazing alloy material 16a in the production step for the Cu--Mo
substrate. Such an Sn--Cu-type brazing alloy material having a Cu
base bonded thereto can be obtained in a similar manner to the
second method above, where a clad composite 15 (see FIG. 4(b)) is
produced in which Sn--Cu-type alloy layers are bonded to both faces
of an Mo base, for example. According to this method, a Cu--Mo--Cu
substrate is obtained, in which a Cu substrate is further provided
on the upper face of the Sn--Cu-type alloy layer 13.
Embodiment 3
[0161] With reference to FIG. 6, an embodiment of a power module 80
having the Cu--Mo--Ni substrate according to the present embodiment
will be described. However, the power module of the present
embodiment is not limited thereto.
[0162] As shown in FIG. 6, in the power module 80, a first Cu--Mo
substrate 30, two ceramic substrates 50a and 50b, four second
Cu--Mo substrates 40a, 40b, 40c and 40d, and four semiconductor
chips (IGBT) 60a, 60b, 60c and 60d are stacked in this order.
Electrical connections between the semiconductor chips 60a and 60b,
and between 60c and 60d are provided via Al wires 70a and 70b,
respectively.
[0163] The first Cu--Mo substrate 30 includes: a Cu base 21 having
a thickness of about 3 mm; and two Mo bases 22a and 22b which are
locally present on the Cu base 21 (each having a thickness of about
0.6 mm). The surfaces of the Mo bases 22a and 22b are covered with
Sn--Cu-type alloy layers 23a and 23b, respectively, each having a
thickness of about 20 .mu.m, whereby enhanced heat-releasing
characteristics and an enhanced adhesion with an Ni plating layer
24 are obtained. The surface of the first Cu--Mo substrate 30 is
covered with the Ni plating layer 24 having a thickness of about 5
.mu.m, whereby an enhanced brazability with the ceramic substrates
50a and 50b is obtained.
[0164] The second Cu--Mo substrates 40a and 40b, and 40c and 40d
are provided on the Mo bases 22a and 22b, respectively, via the
ceramic substrates 50a and 50b. Since the second Cu--Mo substrates
40a, 40b, 40c and 40d are all identical in construction, the
following description will be directed to the second Cu--Mo
substrate 40a.
[0165] The second Cu--Mo substrate 40a includes: a Cu base 31a
having a thickness of about 2 mm; and an Mo base 32a being locally
present on the Cu base 31a and having a thickness of about 0.5 mm.
The surface of the Mo base 32a is covered with an Sn--Cu-type alloy
layer 33b having a thickness of about 20 .mu.m, whereby enhanced
heat-releasing characteristics and an enhanced adhesion with an Ni
plating layer 34a are obtained. The surface of the second Cu--Mo
substrate 40a is covered with the Ni plating layer 34a having a
thickness of about 3 .mu.m, whereby an enhanced brazability with
the ceramic substrate 50a and the semiconductor chip 60a is
obtained.
[0166] Although FIG. 6 illustrates an exemplary Cu--Mo substrate
40a in which all surface of the Mo base 32a is covered with the
Sn--Cu-type alloy layer 33a, this is not a limitation. For example,
a Cu--Mo substrate may be used in which only the exposed surface
region (an upper face and side faces) of the Mo base 32a is covered
with the Sn--Cu-type alloy layer 33a.
[0167] Solder layers 51 and 52 (e.g., Sn--Pb) are used for bonding
between the first Cu--Mo substrate 30 and the ceramic substrate
50a, and between the ceramic substrate 50a and the second Cu--Mo
substrates 40a and 40b, respectively. On the other hand, solder
layers 53a and 53b (e.g., Ag--Cu) are used for bonding between the
second Cu--Mo substrates 40a and 40b and the semiconductor chips
60a and 60b.
[0168] Next, a production method for the power module 80 of the
present embodiment will be described.
[0169] As shown in FIG. 6, the power module 80 of the present
embodiment has two equivalent multilayer structures provided on the
Cu base 21. Hereinafter, for convenience of explanation, the
construction on the right-hand half (A in the figure) of FIG. 6
will be focused.
[0170] First, by the first method according to Embodiment 1 above,
the first Cu--Mo substrate 30 and the second Cu--Mo substrates 40a
and 40b are produced. Next, by electroless plating technique, an Ni
plating layer is provided so as to cover each surface. The details
of the electroless plating technique will be described in
connection with the Examples set forth below.
[0171] Then, the first Cu--Mo substrate 30 and the ceramic
substrate 50a are bonded together. Specifically, for example, a
Cu--Ag-type brazing material is placed between the first Cu--Mo
substrate 30 and the ceramic substrate 50a, and heat-melted. The
type of brazing material is not limited thereto, and any known
brazing material that is capable of bonding together the Cu--Mo
substrate 30 and the ceramic substrate 50a may be used. The heating
temperature may be determined as appropriate according to the type
of brazing material used.
[0172] Furthermore, the second Cu--Mo substrates 40a and 40b and
the semiconductor chips 60a and 60b are bonded together,
respectively. Specifically, for example, pieces of an Ag--Cu-type
brazing material are placed between the second Cu--Mo substrates
40a and 40b and the semiconductor chips 60a and 60b, and
heat-melted to effect bonding. As for the type of brazing material,
any known brazing material that is capable of bonding together the
Cu--Mo substrates 40a and 40b and the semiconductor chips 60a and
60b can be used. The heating temperature may be determined as
appropriate according to the type of brazing material used.
[0173] Next, the ceramic substrate 50a having the first Cu--Mo
substrate 30 bonded thereto and the second Cu--Mo substrates 40a
and 40b having the semiconductor chips 60a and 60b bonded thereto
are bonded together. Specifically, for example, pieces of an
Sn--Pb-type brazing material are placed between the ceramic
substrate 50a and the second Cu--Mo substrates 40a and 40b, and
heat-melted. The type of brazing material is not limited thereto,
and any known brazing material that is capable of bonding together
the ceramic substrate 50a and the Cu--Mo substrates 40a and 40b may
be used. The heating temperature may be determined as appropriate
according to the type of brazing material used.
[0174] (Cu--Mo Multilayer Plate)
[0175] A Cu--Mo multilayer plate according to an embodiment of the
present invention includes a Cu base, an Mo base, and an
Sn--Cu-type alloy layer containing no less than 1 mass % and no
more than 13 mass % of Sn, which are positioned in this order. A
further Sn--Cu-type alloy layer containing no less than 1 mass %
and no more than 13 mass % of Sn may be provided between the Cu
base and the Mo base (bonding surface).
[0176] The Cu--Mo multilayer plate according to the present
embodiment differs from the above-described Cu--Mo substrate
according to the present embodiments in that no Sn--Cu-type alloy
layer exists on the side faces of the Mo base. Such a Cu--Mo
multilayer plate may be useful as a material for producing a Cu--Mo
substrate, for example.
EXAMPLES
[0177] With the methods of Experimental Examples 1 to 7 described
below, Cu--Mo--Ni substrates were produced each having an Ni
plating layer on the surface of a Cu--Mo substrate, and their
exterior appearances were compared.
Experimental Example 1
[0178] Herein, by using a Cu--Mo clad composite, a Cu--Mo substrate
having an Sn--Cu-type alloy layer provided in an exposed surface
region (an upper face and side faces) of Mo was produced (Inventive
Example 1). The Cu--Mo clad composite was produced by stacking
together the Cu base 1 and the Mo base 2 and subjecting them to hot
rolling (thickness of the Cu base: 0.63 mm; thickness of the Mo
base: 0.63 mm).
[0179] Next, an Sn--Cu-type brazing alloy foil (thickness: 25
.mu.m) containing about 2 mass % of Sn was provided. The
Sn--Cu-type brazing alloy foil had a melting point of about
950.degree. C.
[0180] The Sn--Cu-type brazing alloy foil thus obtained was placed
on the upper face of the Cu--Mo clad composite (or strictly
speaking, on the Mo base), and heated at a temperature of about
99.degree. C. for about 3 minutes. Through the heating, the
Sn--Cu-type brazing alloy foil was melted, and a Cu--Mo substrate
was obtained in which the upper face and side faces of the Mo base
were covered with an Sn--Cu-type alloy layer having a thickness of
about 20 .mu.m. The Sn content in the Sn--Cu-type alloy layer was
generally in the range from 1.1 mass % to 2.5 mass %.
[0181] Next, following the procedure from (1) to (4) below, an Ni
plating layer having a thickness of about 3 .mu.m to 5 .mu.m was
formed on the surface of the Cu--Mo substrate.
[0182] (1) Degreasing with ethanol (at room temperature for 1
minute)
[0183] (2) Etching with sulfuric acid hydrogen peroxide (a solution
in which sulfuric acid, hydrogen peroxide, and water was mixed at a
volume ratio of 10:5:85) (at 30.degree. C. for 5 minutes)
[0184] (3) Introduction of a catalytic metal to the Cu--Mo
substrate
[0185] Apply an Sn catalyst (at room temperature for about 5
minutes).fwdarw.Apply a Pd--Sn complex catalyst (at room
temperature for about 5 minutes).fwdarw.Apply a Pd catalyst (at
room temperature for about 3 minutes)
[0186] (4) Formation of an Ni plating layer
[0187] By using an electroless Ni plating bath (sulfuric acid Ni:
30 g/L; sodium hypophosphite: 10 g/L; sodium acetate: appropriate
amount; pH: about 4.6) of the below-described composition, plating
was performed at 80.degree. C. for 30 minutes.
Experimental Example 2
[0188] For comparison, a Cu--Mo substrate was subjected to
electroless Ni plating in a manner similar to the method described
in Patent Document 1.
[0189] Specifically, the same type of Cu--Mo clad composite as that
of Experimental Example 1 was provided, and an Ni plating layer was
formed by using an electroless Ni plating bath as described in
Experimental Example 1.
Experimental Example 3
[0190] For reference sake, a Cu--Mo substrate was subjected to a
conventional Ni plating treatment.
[0191] Specifically, the same type of Cu--Mo clad composite as that
of Experimental Example 1 was provided, and an Ni plating layer was
formed by the following procedure.
[0192] First, the Cu--Mo clad composite was immersed (at room
temperature for about 10 seconds) in an etchant containing about
200 g/L to 250 g/L of potassium ferricyanide, thus etching its
surface.
[0193] Next, on the Cu--Mo clad composite having been thus etched,
an Au coating was deposited to a thickness of about 0.1 .mu.m by
sputtering technique. The sputtering was performed under a bias
voltage of about 1 kV to 5 kV for about 30 minutes, while
controlling the pressure within the vacuum container at about
10.sup.-1 Pa.
[0194] Next, the Cu--Mo substrate having the Au coating deposited
thereon was subjected to a diffusion heat treatment at about
700.degree. C. for 10 minutes in an H.sub.2 atmosphere.
[0195] Thereafter, an Ni plating layer was formed according to the
procedure of (1) to (4) described in Experimental Example 1.
Experimental Example 4
[0196] An Ni plating layer was formed through the same procedure as
that of Experimental Example 1, except that an Sn--Cu-type brazing
alloy foil (melting point: about 940.degree. C.) containing 5 mass
% of Sn was used. Note that the heat treatment for forming the
Sn--Cu-type alloy layer was performed at a temperature about
4.degree. C. to about 5.degree. C. which was higher than the
melting point of the brazing foil used. This also applies to
Experimental Examples 5 to 7 below.
Experimental Example 5
[0197] An Ni plating layer was formed through the same procedure as
that of Experimental Example 1, except that an Sn--Cu-type brazing
alloy foil (melting point: about 810.degree. C.) containing 13 mass
% of Sn was used.
Experimental Example 6
[0198] For comparison, an Ni plating layer was formed through the
same procedure as that of Experimental Example 1, except that an
Sn--Cu-type brazing alloy foil (melting point: about 800.degree.
C.) containing 14 mass % of Sn was used.
Experimental Example 7
[0199] For comparison, an Ni plating layer was formed through the
same procedure as that of Experimental Example 1, except that an
Sn--Cu-type brazing alloy foil (melting point: about 1000.degree.
C.) containing 0.5 mass % of Sn was used.
[0200] (Evaluations)
[0201] The exterior appearance of the Cu--Mo substrates obtained
according to Experimental Examples 1 to 7 was observed by visual
inspection. Hereinafter, the Cu--Mo substrates obtained according
to Experimental Examples 1 to 7 will be referred to as Inventive
Example 1, Comparative Example 1, and Conventional Example,
Inventive Example 2, Inventive Example 3, Comparative Example 2,
and Comparative Example 3, respectively.
[0202] In Inventive Examples 1 to 3, the upper face and side faces
of the Mo base are covered with a predetermined Sn--Cu-type alloy
layer, and therefore no bulging of the substrate or peeling of the
Ni plating layer was observed. Moreover, a cross section (about 4
cm.sup.2) of each of Inventive Examples 1 and 2 was observed with
an optical microscope (magnification .times.10), whereby no voids
were found in the Sn--Cu alloy layer and the Ni plating layer. In
Inventive Example 3, five minute voids with a diameter of 30 .mu.m
to 80 .mu.m were found in the Sn--Cu alloy layer and the Ni plating
layer, which were ascribable to partial oxidation of Sn or elution
of a minute amount of Sn during plating, but no bulging or peeling
was found.
[0203] On the other hand, in Comparative Example 1, the Ni plating
layer was not formed with good adhesion, and bulging was observed
in a portion of the surface. In Comparative Example 2, the Ni
plating layer was formed with good adhesion, but seven bulges with
a diameter of 100 .mu.m or more were observed in portions of the
surface. In Comparative Example 3, a portion of the base Cu melted
during brazing, the Ni plating layer was not formed with good
adhesion, and five bulges with a diameter of about 100 .mu.m were
observed in the face which was in contact with the Mo base.
[0204] On the other hand, in Conventional Example, the Ni plating
layer was formed with good adhesion on the surface of the Mo base,
but bulging occurred in a portion of the Cu base that was not in
contact with the Mo base, and peeling of the Ni plating layer was
observed.
[0205] (Sn Distribution in the Sn--Cu-Type Alloy Layer)
[0206] With respect to Inventive Example 1, the Sn concentration in
a cross section, taken along the thickness direction, of the
Sn--Cu-type alloy layer formed on the upper face of the MO base was
measured by EPMA analysis. Specifically, in a cross-sectional
photograph of the Cu--Mo--Ni substrate shown in FIG. 7, the Sn
concentration was measured in a total of five points (portions
indicated with arrows 1 to 5 in the figure). The results are shown
in Table 1.
TABLE-US-00001 TABLE 1 points of measurement number depth from in
Ni plating layer Sn amount FIGURE (mm) notes (mass %) 1 0.0025
generally -- central portion of Ni plating layer 2 0.005 interface
between 2.47 Ni plating layer and alloy layer 3 0.010 within alloy
layer 1.37 4 0.016 within alloy layer 1.15 5 0.025 interface
between 1.40 alloy layer and Mo base
[0207] As shown in Table 1, it was found that Sn in the Sn--Cu-type
alloy layer formed on the upper face of the Mo base exists in
highest concentration at the interface between the Ni plating layer
and the Sn--Cu-type alloy layer, rather than being uniformly
distributed throughout the alloy layer. The presumable reason is
that, as mentioned earlier, Sn is likely to be oxidized and
migrates toward the surface of the Sn--Cu-type alloy layer during
the process of forming the Sn--Cu-type alloy layer. However, from
the Mo base side toward the Ni plating layer side, the Sn
concentration undergoes stepwise increases as shown in Table 1,
rather than gradually increasing.
[0208] Although an Sn concentration in the Cu--Mo--Ni substrate
having the Ni plating layer formed thereon was measured herein, it
has been experimentally confirmed that a similar trend is also
observed in the Cu--Mo substrate before the Ni plating layer is
formed.
INDUSTRIAL APPLICABILITY
[0209] The Cu--Mo substrate according to the present invention is
suitably used as a heat spreader for a power module to be mounted
in an automobile or the like, for example.
* * * * *